GENERAL CHARACTERISTICS AND GEOLOGICAL HISTORY 367 



Table 147 



River Ca 2+ Mg 2+ Na+ + K + 



in% in% in% 



Amu-Darya 83-1 17-6 11-12 2-4 43-4 9-2 



Syr-Darya 87-6 16-1 20-6 3-8 43-8 80 



River HC0 3 - S0 4 2 CI- Sum of 



in% in% in% ions 



Amu-Darya 153-5 32-6 104-9 22-3 74-1 15-7 470-8 



Syr-Darya 186-1 35-1 164-4 30-2 40-3 7-4 543-8 



III. SOME PECULIARITIES OF THE DEVELOPMENT OF 

 FAUNA AND FLORA 



General features 



The palaeogeographic changes discussed above in the seas which covered the 

 southern part of Europe and Asia during the Tertiary and Quaternary Periods 

 influenced their fauna in a radical way, primarily through loss of salinity 

 which was at times very considerable. 



The genetic heterogeneity of the fauna of our southern seas is the result 

 of their history. 



Relict community 



The so-called ancient autochthonous community — the originally marine 

 Tertiary fauna elaborated by the fresher-water phases — may perhaps have 

 had a variety of origins. The marine fauna had several opportunities of 

 breaking into the bodies of water which occupied the area of the Black and 

 Caspian Seas. Most characteristic of the Caspian autochthonous fauna are 

 the families and genera of the Porifera Mecznikowiidae, the hydroids Cordy- 

 lophora, the jelly-fish Caspionema and Ostroumovia, the molluscs Cardiidae 

 (Adacna, Monodacna, Didacna), Dreissensiidae, Hydrobiidae (Microme- 

 lania, Caspia, Clessiniola, Hydrobia, Theodoxus), the polychaetes Hypania, 

 Hypaniola, Parhypania, the crustaceans Pontogammarus, Corophium, 

 Gmelina, Amathillina, Pseudocuma, Mesomysis, Paramysis, Metamysis, 

 Astacus, the bryozoans Victorella, the fish Acipenseridae,* Caspialosa, 

 Clupeonella and Gobiidae. This autochthonous community in the main 

 evolved from the marine fauna of the Tethys, which had spread its relicts 

 throughout the brackish and fresh bodies of water of southeastern Europe 

 and central Asia (including the Baikal and Okhrida lakes, the fauna of which 

 is akin to that of the Caspian Sea). This autochthonous community, domin- 

 ant in the Caspian Sea, is concentrated in the least saline parts of the more 

 saline Black-Azov Sea basin in the firths, river-mouths and the eastern part of 

 the Gulf of Taganrog, while the open parts of the Black and Azov Seas are 



* The weight of evidence, however, suggests the derivation of Acipenseridae from fresh 

 water. 



